1. Field of the Invention
This invention relates to a system and method for sampling data in applications including but not limited to high-speed data communications.
2. Description of the Related Art
Digital communication systems operate by sampling an analog signal carried over any one of a variety of transmission media. The transmission medium may be a wire line, an optical fiber, or the air in the case of wireless communication systems. As technology advances, faster data rates will be required in order to satisfy new applications. To be compatible with these applications, digital systems must be able to accurately sample analog signals transmitted at the increased data rates.
SONET networks are a preferred type of high-speed optical communication system in use today. In order to sample signals from these networks, an optical interconnect system is usually employed. In such a system, an optical data stream is converted into an electrical signal and then amplified and sampled.
This sampling operation can be easily performed at low speeds (typically less than 10 Gb/s per channel) by conventional systems using, for example, a flip-flop controlled by a recovered clock at the data rate frequency. Sampling, however, becomes increasingly problematic when the setup time of the flip-flop becomes a significant portion of the duration of a transmitted symbol.
For example, at 20 Gb/s, the symbol duration is 50 ps which means the sampling window itself is about 20 ps, taking a 15 ps slope into consideration. Because flip-flops typically exhibit setup and hold times of 10 ps or above, they cannot be used to reliably sample data streams at faster data rates, e.g., 20 Gb/s or above. Moreover, the converted signal output from the front-stage amplifier of these conventional systems is an analog signal that does not necessarily reach determined logical levels with any degree of consistency. This may be attributable to optical power variations which make it difficult to reliably sample data using a flip-flop.
Optical systems are by no means the only ones that suffer from these drawbacks. Other types of communication systems also experience unacceptable performance when attempting to sample high-speed data streams.